In the past, iOS would allow users to download apps while connected to cell networks only if the app was less than 50 MB in size. To download a larger app, users had to wait until they were connected to WiFi. As a result, most free apps are just under 50MB.
With iOS 7, Apple has upped that limit to 100MB. With the change, many mobile development pros will soon be increasing the size of their apps to add more features, improved graphics and other benefits. The unintended consequence could be that more users will exceed their monthly data download limits.